PAR-02-049 (R-03), 23. Tools for research on the genetics and proteomics of aging. Gene targeting is a powerful toll for the studies of in vivo gene functions. However, potential problems such as deficits in early development or functional compensation of the missing gene have dramatically complicated the interpretation and in particularly limited its utility in the studies of aging. In this proposal, we develop a novel conditional (inducible/reversible) mRNA knockout technique. My long-term goal is to understand the roles of genes in cognitive behavioral processes as well as in the pathogenesis of age-related brain diseases. The specific aims of this proposal are: (1) to design a special transposon vector system that is able to tag and regulate any gene of interest in a conditional fashion. The theoretical basis for this system is that both trans- and cis-acting are the essential mechanism for gene transcription. The transposon, consisting of tTA, a stop signal, and tetO, is designed to insert into the genome by homologous recombination in such a way that tTA (trans-acting) is downstream to the endogenous promoter of any gene of interest followed by a stop sequence to silence the endogenous gene transcription. In turn, the endogenous gene (or its cDNA) is switched downstream of tetO (cis-acting) promoter. Thus, the targeted gene expression could be switched off or on by the treatment with or withdrawal of a inducer. The most striking promise of this system is to allow one to temporally associated mRNA transcription with any biological or behavioral processes. (2). to establish a small library of gene targeted transposon-tagged ES cell lines. At the first stage, we will produce preseniline-1 and BDNF transponson-tagged ES cell lines and their knockout mice to validate this system. Later on, based on the feasibility of this system and the fast progress in mouse genome project, it is reasonable to establish a small library with 20-40 ES lines. The proposal is significant, because it capitalizes on a new idea to produce conditional mRNA knockout mice and it will be particularly useful for the studies of cognitive behaviors during aging. In addition, the distribution of these ES cell lines into the research community will significantly strengthen nation-wide efforts on the studies of functional genomics, as well as gene functions in relation to aging processes.